Blender Render: Python material
I found out what I did wrong. The documentation of materials on the blender api page did not mention "get", but the bpy_struct said you can use "get" in the function, so:

mat = bpy.data.materials("Abc")


Should be:

mat = bpy.data.materials.get("Abc")


Also I have to define what scene of scene.frame_current is.
That means at the beginning, I need to import bpy.

import bpy
scene = bpy.context.scene


Also default_value is nonsense to be placed there. Being the diffuse color that's had its keyframe changed, it should be:

mat.keyframe_insert(data_path="diffuse_color", frame=scene.frame_current)


In conclusion, it should look like this:

import bpy
scene = bpy.context.scene

mat = bpy.data.materials.get("Abc")
mat.diffuse_color = (1.0,0.0,0.0)
mat.keyframe_insert(data_path="diffuse_color", frame=scene.frame_current)